In reference to Heartbreaker I myself always played two hands on the hi-hat also. I think there is overdubbed percussion on that track. There is that famous photo in the studio of of Jones, Plant, and Bonham playing various percussion instruments, I don't think it's a far reach that maybe they overdubbed something there. But I agree about the live recordings of this tune he is not playing two hands on the hi-hat, it's pretty straight forward. I like the live versions better, it is a faster tempo then the studio track. When I play this song out I usually play the BBC recordings version.
I have a question in reference to "Ramble On" since we are talking about Led Zeppelin II. Does anyone know what that subtle tapping noise is throughout the song? What is Bonham playing on or is it electronically produced? To me it almost sounds like a towell on top of maybe a floor tom, or sometimes it sounds like he is tapping on a phonebook (ha ha.)